Troubleshoot connectivity issues in SQL Server
Applies to: SQL Server
Original KB number: 4009936
There are various causes for connectivity issues in SQL Server. This article series helps you troubleshoot the most common SQL Server connectivity issues and describes the tools and methods you can use for troubleshooting.
If multiple SQL Server instances in your environment are impacted, or the issue is intermittent, it usually indicates Windows policy or networking issues. Although this series of articles provides guidance, it may not effectively troubleshoot some specific scenarios.
Before you start troubleshooting, check Recommended prerequisites and checklist for troubleshooting connectivity issues for logs that you should collect to assist with troubleshooting. There's also a list of quick actions to avoid common connectivity errors when working with SQL Server.
Common connectivity issues
Use the list below to navigate to the appropriate article page for detailed troubleshooting steps for your scenario:
Covers the following Login errors:
- "Login failed for user 'NT AUTHORITY\ANONYMOUS LOGON'"
- "Login failed for user '(null)'"
- "Login failed for user (empty)"
- "Login failed for user '<username>'"
- "Login failed for user '<domain>\<username>'"
Tools and methods that help you troubleshoot connectivity issues
The following articles provide details for various tools and procedures to troubleshoot different connectivity errors:
Describes how to configure Windows firewall for successful connections to instances.
Describes how to test connections between SQL Server and clients using UDL files.
Describes how to use the PortQryUI tool (a graphical user interface (GUI) port scanner) to help troubleshoot connectivity issues.
Provides steps to check whether SQL Server is listening on dynamic or static ports.
Describes how to use Kerberos Configuration Manager to fix Service Principal Name (SPN) issues.